The invention relates to a method of nuclear magnetic resonance (NMR) tomography for investigating a target object, wherein radio frequency (RF) pulses are irradiated into a target volume and/or RF pulses from the target volume are detected, wherein the target volume is determined by the frequency of the RF pulses and/or through magnetic field gradients, and wherein the target object is moved relative to the NMR tomograph during NMR data acquisition.
NMR tomography methods with moving target objects are known from Kruger et al., Magnet. Reson. Med. 47 (2002), 224, and also from Scheffler, Proc. 9th Meeting ISMRM, Glasgow (2001), 1774.
NMR tomography is mainly used for medical diagnostics to obtain information about the volume (i.e. the inside) of a target object, in particular about diseased or possibly diseased regions of a human body thereby utilizing the interaction between nuclei and electromagnetic pulses.
NMR images are typically acquired in individual flat slices. To investigate larger target objects, individual recordings of several slices of the target object can be produced. When one slice is completely recorded, the target object is displaced slightly perpendicularly to the slice plane relative to the NMR tomograph and a further slice is subsequently recorded. In these simple cases, the target object is immobile during the actual NMR data acquisition.
Recording methods of objects which are moved during the NMR data acquisition (mainly for use for so-called total body imaging) are known from literature (see e.g. Kruger et al, Magnet. Reson. Med. 47 (2002), 224) which use different principles. Methods were developed wherein the motion occurs within the recording plane (i.e. the slice). With stationary magnetic field gradients, such motions produce primarily displacement of the recording data relative to the recorded target object. When recording methods are used which are based on repeated recording of in each case differently locally encoded signals, this displacement differs in correspondence with the continuous motion of the object from one recording step to the next. This displacement can be compensated for through corresponding data post-processing when the displacement speed is known.
Methods for recording images during motion perpendicular to the recording plane are also known (see e.g Scheffler, Proc. 9th Meeting ISMRM, Glasgow, (2001), page 1774). In the conventional methods, the displacement speed is thereby selected such that the inconsistency of the data due to the displacement remains small thereby hardly influencing the recording quality. In general, these methods are carried out such that the motion advance over an image acquisition is small compared to the thickness of the selected volume (i.e. the volume to be investigated). Fast acquisition techniques such as e.g. trueFISP or gradient echo sequences are used for such recording methods, which are largely stable compared to image artefacts caused by motion. These methods still have the disadvantage that the small motion advance prolongs the overall duration of the NMR investigation.
In contrast thereto, it is the underlying purpose of the present invention to present a method for investigating a target object, which moves relative to the NMR tomograph during NMR data acquisition, which can be carried out in a fast and simple fashion.